Structural members are available in a wide variety of configurations to provide structural support under a variety of loading conditions. For example, a fuselage portion of an aircraft typically includes parallel and longitudinally oriented structural members called keel beams that impart flexural stiffness to the fuselage, particularly in a region where the wing assemblies of the aircraft are joined to the fuselage. Typically, a structural member, such as an aircraft keel beam, is fabricated from aluminum or titanium, and is configured to resist high flexural loads. Accordingly, the structural member may contribute substantially to the overall weight of the aircraft structure.
Reinforced polymer-based materials are also available, and may be used to form various structural members. Such materials may be used as a substitute for metals particularly in applications where relatively low weight and high mechanical strength is desired. As a result, reinforced polymer-based materials are widely used in a variety of commercial and military aircraft, terrestrial vehicles and consumer products. The material is generally comprised of a network of reinforcing fibers that are generally applied in layers, and a polymeric resin that substantially wets the reinforcing fibers to form an intimate contact between the resin and the reinforcing fibers. The material may then be formed into a structural component by a variety of known forming methods, such as an extrusion process or other forming processes.
Structural members formed from reinforced polymer-based materials are generally more expensive to fabricate, and more difficult to inspect and repair than corresponding structural members formed from metals. In particular, repair methods for metallic structural members that have sustained in-service damage due to excessive loading, or have sustained fatigue and/or corrosive damage while in service, are well developed.
What is required is a structural member that is easily and inexpensively fabricated, provides a favorable flexural strength to weight ratio in comparison to conventional structural members, and may be easily assembled, inspected and repaired.